An automated sequential injection analysis spectrophotometric assay for the determination of purine alkaloids in
coffee drinks was developed. The sample was treated with a
carrez reagent for matrix suppression followed by filtration;
subsequently, alkaloids were separated from organic acids
using a short C18 monolithic column (10 × 4.6 mm). The flow
rate of the separation step was 10 μL s−1 with 10% v/v of
methanol as the mobile phase. The sum of alkaloids evaluated
as caffeine was detected at 274 nm. The influence of the main
parameters affecting the quantification of purine alkaloids was
optimized. One sample analysis lasted 15 min when aspirated
in triplicate. The linear range was 1–15 mg L−1, and the determination coefficient (r2) was 0.9969. The limit of detection
and limit of quantitation were 0.128 and 0.425 mg L−1, respectively. The repeatability evaluated as the relative standard
deviation (RSD) was 3.58% (n = 12, 10 mg L−1). Under optimal conditions, the method was successfully applied to determine purine alkaloids in different real samples including
soluble coffee, coffee from an espresso machine, and brewed
coffee drinks.

• Automated Sequential Injection Method for Determination of Caffeine in Coffee Drinks